Firefighters battling the largest wildfire in Texas history face increasingly difficult weather conditions on Saturday.

The Smokehouse Creek Fire that began Monday has killed at least two people, left a charred landscape of scorched prairie, dead cattle and destroyed as many as 500 structures, including burned-out homes, in the Texas Panhandle.

The National Weather Service in Amarillo has issued a red flag warning for the entire Panhandle from late Saturday morning through midnight Sunday after rain and snow on Thursday allowed firefighters to contain a portion of the fire.

“A combination of strong winds, low relative humidity and warm temperatures will create favorable weather for rapid fire growth and spread,” according to the weather service’s forecast.

“Critical fire weather conditions are expected to return … as winds out of the southwest gust to 40 to 45 mph and humidity drops below 10 percent,” the forecast said, with a high temperature of 75 degrees F (24 degrees C).

The fire, which has merged with another fire and crossed the state line into western Oklahoma, has burned more than 1,700 square miles (4,400 square kilometers) and was 15% contained, the Texas A&M Forest Service said Friday.

The cause of the fire remains under investigation, although strong winds, dry grass and unseasonably warm weather fed the flames.

“Everybody needs to understand that we face enormous potential fire dangers as we head into this weekend,” Republican Gov. Greg Abbott said Friday after touring the area. “No one can let down their guard. Everyone must remain very vigilant.”

Two women were confirmed killed by the fires this week. But with flames still menacing a wide area, authorities haven’t yet thoroughly searched for victims or tallied homes and other structures damaged or destroyed.

Two firefighters were injured battling the flames in Oklahoma. One suffered a heat-related injury and the other was injured when the brush pumper he was riding in struck a tanker truck as the two were heading to fight the fire near Gage.

Both firefighters are expected to recover.

Texas Agriculture Commissioner Sid Miller said individual ranchers could suffer devastating losses due to the fires, but predicted the overall impact on the Texas cattle industry and consumer beef prices would be minimal. The fires are leaving “dead animals everywhere,” Texas Rep. Ronny Jackson said in a video update on Wednesday.

Dozens of Texas counties have been under a burn ban since earlier in the week, according to the Texas A&M Forest Service.